Pattern defect inspection apparatus and method

ABSTRACT

A pattern defect inspection apparatus capable of detecting minute defects on a sample with high sensitivity without generating speckle noise in signals is realized. Substantially the same region on a surface of a wafer is detected by using two detectors at mutually different timings. Output signals from the two detectors are summed and averaged to eliminate noise. Since a large number of rays of illumination light are not simultaneously irradiated to the same region on the wafer, a pattern defect inspection apparatus capable of suppressing noise resulting from interference of a large number of rays, eliminating noise owing to other causes and detecting with high sensitivity minute defects on the sample without the occurrence of speckle noise in the signal can be accomplished.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 12/781,682filed May 17, 2010 now U.S. Pat. No. 8,233,145, which is a continuationof application Ser. No. 12/113,781 filed May 1, 2008 now U.S. Pat. No.7,746,453. The present application also claims priority from Japanesepatent No. 2007-121741 filed on May 2, 2007, the contents of which arehereby incorporated by reference into this application.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a pattern defect inspection apparatus fordetecting defects and foreign matters of a circuit pattern on a sample.

2. Description of the Related Art

Foreign matters and defects (short-circuit, wire breakage, etc) on asemiconductor wafer, if any, will result in insulation defects andshort-circuits of wires and capacitors and film breakage of gate oxidefilms and eventually, in the defects of semiconductor devices insemiconductor production processes.

Structures of semiconductor devices have got more and more diversifiedand complicated in recent years. Semiconductor devices are classifiedinto memory products that are constituted mainly of repetition patternsand logic products that are constituted mainly of non-repetitionpatterns, for example. Since product life of the semiconductor deviceproducts is relatively short, the production yield must be improvedwithin a short period. It has thus become more important to reliablyfind out so-called “target defects” that must be managed duringfabrication of the semiconductor devices.

The “target defect” includes voids and scratches in a CMP process inaddition to foreign matters and pattern defects in a production processof each of film formation, etching and photolithography. The targetdefect includes further short-circuit and bridge in gate wiring andmetal wiring portions such as aluminum and non-conduction andnon-opening of contact apertures that connect wires.

SEM (Scanning Electron Microscope) inspection technology and opticalinspection technology are generally known as technology for detectingthe target defects on the semiconductor wafer described above. Theoptical inspection technology is divided into bright visual fieldinspection technology and dark visual field inspection technology. Thebright visual field inspection technology illuminates a wafer through anobjective lens and condenses reflected and diffracted rays of light by acondenser lens. The rays of light so diffracted are subjected tophotoelectric conversion by detectors and defects are detected by signalprocessing. On the other hand, the dark visual field inspectiontechnology illuminates a wafer from outside NA (Numerical Aperture) ofan objective lens and condenses scattered rays of light by an objectivelens. The rays of light so condensed are subjected to signal processingto detect defects in the same way as in the bright visual fieldinspection technology.

As one of the optical type dark visual field inspection technologies,JP-A-62-89336, for example, describes a detection method that makes itpossible to detect foreign matters and defects with high sensitivity andhigh reliability by irradiating a laser beam onto a wafer, detectingscattered rays of light from the foreign matters and comparing theresult with an inspection result of the same kind of wafer inspectedimmediately before to eliminate false information due to patterns.

As the technology for inspecting the foreign matters described above,JP-A-1-117024, JP-A-4-152545 and JP-A-5-218163, for example, describe adetection method that irradiates coherent light to a wafer, removes therays of light generated from repetition patterns on the wafer by using aspatial filter, and stresses and detects those foreign matters anddefects which do not have repetition characteristics.

A method for detecting minute foreign matters by irradiating light tothe same point from multiple directions and detecting scattered rays oflight at mutually different angles is known, too (JP-A-11-258157, forexample).

SUMMARY OF THE INVENTION

Foundation patterns below the position at which the defect occurs havegot diversified in recent years in addition to the reduction of the sizeof defects themselves (below resolution of an optical system) and theirdiversification. Consequently, detection of the target defect has becomemore difficult. Factors that impede the detection of the target defectinclude grains of metal wires such as aluminum, minuteconcavo-convexities of a surface called “morphology”, non-uniformity ofthe intensity of interference light due to a very small difference ofthe film thickness of transparent films (transparent to an illuminationwavelength) such as an insulating film, roughness of edge portions ofwiring, and so forth.

Development of high NA of an objective lens for inspection and opticalsuper resolution technology has been made as the optical inspectiontechnology. However, because the high NA of the objective lens forinspection has reached a physical limit, an essential approach is toreduce the wavelength of illumination light to UV (Ultra Violet) lightand DUV (Deep Ultra Violet) light. To increase light power of the raysof light emitted from a minute target defect, on the other hand, anillumination light source having high luminance is necessary. Therefore,a laser beam source is used in many cases as the illumination lightsource to acquire illumination light having high luminance in the UV andDUV ranges.

When the laser beam source having such high luminance is used in theprior art technology, however, speckle noise owing to interference ofillumination light such as the laser beam source invites the increasesof variance of signals detected by detectors and results in noise duringsignal processing. Consequently, a minute defect cannot be detectedhighly precisely.

It is therefore an object of the invention to accomplish pattern defectinspection apparatus and method capable of detecting highly preciselyminute defects on a sample without generating speckle noise in signals.

To accomplish the object described above, the invention employs thefollowing construction.

In a defect inspection apparatus for detecting a defect on a samplesurface, a defect inspection apparatus according to the inventionincludes an illuminating unit for illuminating a plurality of regions onthe sample surface; an image forming unit for forming optical images ofthe plurality of regions of the sample surface illuminated; a pluralityof detecting units for detecting the optical images formed and detectingreflected light from the sample surface; and a defect detecting unit forprocessing reflected light detected by the plurality of detecting unitsand detecting a defect on the sample surface.

In a defect inspection apparatus for detecting a defect on a samplesurface, a defect inspection apparatus according to the inventionincludes a multi-direction illuminating unit for illuminating the samplesurface from multiple directions among an azimuth of 360 degrees of thesample surface; an imaging forming unit for forming an optical image ofthe sample surface illuminated by the multi-direction illuminating unit;a plurality of detecting units for detecting the optical image formed bythe imaging unit and detecting reflected light from the sample surface;and a defect detecting unit for processing reflected light detected bythe detecting units and detecting a defect on the sample surface.

It is preferred in the defect inspection apparatus described above thatsubstantially the same region on the sample surface is illuminated atmutually different timings, mutually different detectors detectreflected light from the same region at mutually different timings andthe defect of the same region is detected on the basis of detectionsignals from the mutually different detectors.

The invention can accomplish pattern defect inspection apparatus andmethod capable of detecting highly precisely minute defects on a samplewithout generating speckle noise in signals.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic structural view of a pattern defect inspectionapparatus according to a first embodiment of the present invention;

FIG. 2 shows a detailed construction of an illuminating unit shown inFIG. 1;

FIG. 3 shows in detail a condensing portion of an illumination lightshown in FIG. 1;

FIGS. 4A and 4B show an example of a multi-direction illuminating unit;

FIGS. 5A and 5B are detailed explanatory views of a multi-regiondetecting unit;

FIGS. 6A and 6B are explanatory views useful for explaining an exampleof a spatial filter;

FIGS. 7A and 7B are explanatory views useful for explaining anotherexample of the spatial filter;

FIGS. 8A and 8B show an example where a photo multiplier is used as adetector;

FIG. 9 shows another example where the photo multiplier is used as thedetector;

FIGS. 10A and 10B show an example of the arrangement of the detectors;

FIG. 11 shows signals when the same foreign matter on a wafer isdetected by two detectors;

FIG. 12 is an explanatory view useful for explaining a signal processingcircuit unit;

FIG. 13 shows a schematic construction of an illuminating unit accordingto the second embodiment of the invention;

FIG. 14 shows a schematic construction of an illuminating unit accordingto the third embodiment of the invention;

FIGS. 15A and 15B show an example of a multi-direction illuminating unitin the fourth embodiment of the invention;

FIG. 16 is an explanatory view useful for explaining light condensationin the fourth embodiment of the invention;

FIG. 17 shows an example of a total reflection mirror in the fourthembodiment of the invention;

FIGS. 18A and 18B are detailed explanatory views of a multi-regiondetecting unit in the fifth embodiment of the invention;

FIG. 19 is an overall schematic structural view in the sixth embodimentof the invention;

FIG. 20 is an overall schematic structural view in the seventhembodiment of the invention;

FIG. 21 is an overall schematic structural view in the eighth embodimentof the invention;

FIG. 22 is an explanatory view useful for explaining a bevel portion ofa wafer;

FIGS. 23A and 23B are explanatory views useful for explaining the detailof a bevel inspecting unit;

FIG. 24 is a graph useful for explaining the change of a light receptionquantity of a sheet-like beam receiving unit; and

FIG. 25 is a graph useful for explaining the signal change of a TVcamera for bevel inspection.

DESCRIPTION OF THE EMBODIMENTS

Preferred embodiments of the invention will be hereinafter explained indetail with reference to the accompanying drawings.

First Embodiment

FIG. 1 is a schematic structural view of a pattern defect inspectionapparatus according to the first embodiment of the invention. Theinvention will be hereinafter explained about the case where it isapplied to the inspection of a semiconductor wafer by way of example.

Referring to FIG. 1, the pattern defect inspection apparatus includes aconveying system 2 for supporting and moving a wafer 1 as an inspectionobject, illuminating units 3 and 4, a multi-direction illuminating unit5, an objective lens 6, a multi-region detecting unit 7, a signalprocessing circuit 8, an ADC (Automatic Defect Classification) unit 9,an input/output unit 10, a controller 11 for each unit and relay lensesand mirrors that are not shown in the drawing. Incidentally, arrows(part of which is not shown) extending from the controller 11 to eachunit represents that control signals, etc, are mutually communicated.

Next, the operation will be explained. Beams of illumination lightemitted from the illuminating units 3 and 4 or from the multi-directionilluminating unit 5 are irradiated to the wafer 1. The beams scatteredby a circuit pattern and defects on the wafer are condensed by theobjective lens 6, are subjected to photoelectric conversion by themulti-region detecting unit 7 and are converted to an image signal. Thisimage signal is transmitted to the signal processing circuit 8 and theADC unit 9. Defect detection processing is executed in the signalprocessing circuit 8 and defects on the wafer 1 are detected.

The detection result is transmitted to the ADC unit 9 and to the outputunit 10. On the other hand, the signal sent to the ADC unit 9 issubjected to defect classification processing and the processing resultis sent to the input/output unit 10. The operation described above iscarried out while the wafer 1 is being moved by the conveying system 2and the entire surface of the wafer 1 is inspected.

The input/output unit 10 has an interface function of receiving inputinformation from the user and outputting the information and cantransmit and receive control signals to and from the controller 11.

The detail of each unit will be explained.

To begin with, the detail of the conveying system 2 will be explained.The conveying system 2 includes an X-axis stage 201, a Y-axis stage 202,a Z-axis stage 203, a theta-axis stage 204 and a wafer chuck 205. TheX-axis stage 102 can travel at a constant speed and the Y-axis stage canmove step-wise. All the positions of the wafer 1 can be moved to thecenter of the objective lens 6 by using the X-axis stage 201 and theY-axis stage 202.

The Z-axis stage 203 has the functions of moving up and down the waferchuck 5 and moving the wafer 1 to the focal point of the objective lens6 on the article side on the basis of a signal from an automaticfocusing mechanism that is not shown in the drawing. The -axis stage 204has the turning function of turning the wafer chuck 205 and bringing themoving direction of both X-axis stage 201 and Y-axis stage 202 intoalignment with the turning direction of the wafer chuck 205. The waferchuck 205 has the function of fixing the wafer 1 by adsorbing it byusing vacuum or the like.

The illuminating units 3 and 4 conduct shaping of illumination light toirradiate the wafer 1. The illuminating unit 3 and the illuminating unit4 can illuminate mutually different positions on the wafer 1. Theseilluminating units 3 and 4 include an illumination light source 301,light power polarization adjusting units 302 and 402, coherency reducingunits 303 and 404, light path switching units 304 and 404, condensationoptical systems 305 and 405 and oblique illumination mirrors 306 and406.

FIG. 2 shows a detailed construction of the illuminating units 3 and 4.The illumination light source 301 is a laser light source or a lamplight source. Because the laser light source can shape illuminationlight having high luminance, it can increase light power of scatteredlight from the defect and is effective for high speed inspection.Because the lamp light source has a low interference property, on theother hand, it has the advantage that a speckle noise reducing effect isgreat. The wavelength band of the laser light source may be those ofvisible light, ultraviolet light, deep ultraviolet light, vacuumultraviolet light, extreme ultraviolet light, and so forth. Theoscillation form of laser may be continuous oscillation or pulseoscillation. The wavelength is preferably about 500 nm or below. Forexample, light sources of 532 nm, 355 nm, 266 nm, 248 nm, 200 nm, 193nm, 157 nm and 13 nm can be employed.

It is possible to use, as the laser light source, those which executewavelength conversion of solid YAG laser (wavelength: 1,024 nm) by anon-linear optical crystal and generate second harmonic (SHG), thirdharmonic (THG) and fourth harmonic (FHG) of the fundamental wave,excimer laser, ion laser, and so forth. It is also possible to use alaser light source of the type which causes resonance of two kinds oflight having mutually different wavelengths and oscillates light ofanother wavelength. This is the method that generates sum frequencyresonance of the SHG wave of Ar laser light having a wavelength of 488nm and YAG laser light having a wavelength of 1,064 nm, for example, andoutputs laser having a wavelength of 199 nm. The form of the pulseoscillation laser may be low frequency pulse oscillation laser having anoscillation frequency of several Hz or quasi-continuous wave oscillationpulse laser having an oscillation frequency of dozens to hundreds of Hz.Furthermore, the pulse oscillation method may be either of a Q-switchtype or of a mode lock type.

The advantages of the respective light sources are as follows.

First, the light source having a short wavelength can improve resolutionof the optical system and a high sensitivity inspection can be expected.Solid laser such as YAG does not call for a large scale installation.Therefore, the scale of the apparatus can be reduced and the cost can bedecreased. When pulse oscillation laser having a high frequency is used,the laser can be handled similarly to continuous oscillation laser of ahigh output. Therefore, economical optical components having lowtransmission factors and low reflection factors can be used and aneconomical apparatus can be materialized. Because the coherence distanceis short in the case of laser having a small pulse width, coherency canbe easily reduced time-wise by adding a plurality of light having variedoptical lengths of illumination light.

On the other hand, light sources emitting rays of light in thewavelength range approximate to that of the laser light source can beused as the lamp light source. It is possible to use, for example, a Xelamp, a Hg—Xe lamp, a Hg lamp, a high pressure Hg lamp, a super-highpressure Hg lamp, an Electron Beam-Gas-Emission-Lamp (output wavelength:351 nm, 248 nm, 193 nm, 172 nm, 157 nm, 147 nm, 126 nm and 121 nm, forexample), and the lamp source is required only to output a desiredwavelength. As a selection method of lamps, a lamp having a high outputof a desired wavelength may well be selected and an arc length of thelamp is preferably short. For, the formation of illumination lightbecomes easy.

The light power polarization adjusting unit 302 adjusts illuminationlight power and the polarization direction of illumination light for therays of light emitted from the illumination light source 301. Anattenuator including an ND (Neutral Density) filter, a ½ wavelengthplate and a PBS (Polarized Beam Splitter) is used to adjust light power.A ½ wavelength plate or a ¼ wavelength plate is used to adjust thepolarization direction. After light power and the polarization directionare adjusted, coherency of the ray of light is reduced by the coherencyreducing unit 303 and the ray is branched by the half mirror in theoptical path switching unit 304 to an illumination optical path 2202 andan optical path switching unit 404 or is reflected by a mirror 2201 to amirror 503.

Here, the coherency reducing unit 303 can use a diffusion plate, forexample, but other members can be also used as long as they have thefunction of deviating at random the phase of light. Furthermore, amechanism having the function of changing time-wise the position atwhich illumination light passes may be added.

The ray of light reflected by the half mirror in the optical pathswitching unit 304 to the illumination optical path 2202 is condensed bythe condensation optical system 305 and is irradiated by the obliqueillumination mirror 306 to an illumination region 2204. On the otherhand, the ray of light passing through the half mirror is reflected bythe mirror of the optical path switching unit 404 and travels on anoptical path 2203. In this optical path 2203, illumination light powerand the polarization direction of the ray of light are adjusted.Coherency is reduced by the coherency reducing unit 403 and the ray oflight is condensed in the condensation optical system 405. The ray oflight is then irradiated by the oblique illumination mirror 406 to theillumination region 2205 of the wafer 1. In the first embodiment of thepresent invention, the irradiation direction of the illumination region2204 is a direction having an angle −f relative to the Y direction ofthe wafer 1 and the irradiation direction of the illumination region2205 is a direction having an angle +f relative to the Y direction.

FIG. 3 shows the detail of the condensation portion of illuminationlight. In FIG. 3, the condensation optical system 305 has a cylindricallens 2301 and a relay lens which is not shown in the drawing. The ray oflight condensed by the cylindrical lens 2301 is condensed by the obliqueillumination mirror 306 on the illumination region 2302 on the wafer 1.At this time, illumination light forms an elongated linear illuminationregion in the Y direction. The oblique illumination mirror 306 canrotate with respect to the optical axis and can change the illuminationangle α when its reflection surface is rotated. When the illuminationangle α is changed, however, the oblique mirror 306 can move in the Zdirection lest the position of the illumination region 2302 is changed.Incidentally, the condensation optical system 405 and the obliqueillumination mirror 406 have the same construction as those of thecondensation optical system 305 and the oblique illumination mirror 306,respectively.

Here, the illumination angle α may be decided in accordance with thekind of defects occurring in the inspection object. When detection ismainly directed to foreign matters on the surface of the wafer 1, theillumination angle α is preferably parallel to the wafer surface 1 andis from about 1 to about 5 degrees. When the illumination angle isnearly parallel to the wafer surface 1, an SNR (Signal to Noise Ratio)of the foreign matters on the wafer surface 1 can be improved. Whendetection is mainly directed to a pattern defect or a foreign matterhaving a small height, illumination is preferably made from a highangle. When the angle is too high, however, optical power of reflectionand diffraction from a circuit pattern as a base becomes great and theSNR drops. Therefore, the illumination angle α is preferably from 45 toabout 55 degrees.

To uniformly detect the foreign matter and the pattern defect on thewafer surface 1 described above, an intermediate angle of the anglesdescribed above is preferable and the illumination angle α is preferablyset to about 20 degrees. Furthermore, when a correlation exists betweenthe process of the inspection object and the kind of the defect to bedetected such as when it is known in advance that the defects to bemainly detected in the wiring process are foreign matters having smallheight, decision may be made in advance to the effect that “illuminationis made from a high angle in the wiring process”. The illumination angleof the illuminating unit 3 may be the same as or different from that ofthe illuminating unit 4. These units are preferably used at mutuallydifferent angles when an optimal angle exists depending on the kind ofthe defects as described above.

Next, the multi-direction illuminating unit 5 will be described indetail.

The multi-direction illuminating unit 5 has the functions of conductingillumination from outside the range of NA of the objective lens 6 andfrom multiple directions around the objective lens 6. In other words,this illuminating unit 5 has the function of conducting illuminationfrom multiple directions in the azimuth of 360 degrees of the surface ofthe wafer 1 (sample surface). FIG. 4 shows an example of themulti-direction illuminating unit 5. FIG. 4A is a side view of themulti-direction illuminating unit and FIG. 4B is its top view.

The multi-direction illuminating unit 5 includes a fiber bundle 2401 forintroducing light and a ring-like fiber 2402. The rays of lightreflected by the mirror 305 are introduced by the fiber bundle 2401 intothe ring-like fiber 2402 and illuminate the visual field 2405 of theobjective lens 6 from the direction of 360 degrees around the objectivelens 6. Incidentally, illumination light is condensed at an open angle βto the wafer 1.

Here, the distance from an inlet of the fiber bundle 2401 can be changedwhen light is introduced from the fiber bundle 2401 to the ring-likefiber 2402. In other words, because a luminous flux 2403 is irradiatedto the wafer 1 from the position close to the fiber bundle 2401, itmoves in a short distance inside the ring-like fiber bundle 2402. On theother hand, because a luminous flux 2403 exists on the opposite side tothe luminous flux 2403 while sandwiching the objective lens 6 betweenthem, it moves in a long distance inside the ring-like fiber 2402. Inthis way, the optical path length of illumination light irradiated tothe wafer 1 in each illumination direction can be changed and coherencyof light can be reduced time-wise. Furthermore, because illumination ismade from multiple directions, scattering direction dependence of thedefect and the pattern on the illumination direction can be reduced andstable images can be acquired.

Incidentally, the illuminating unit 3, the illuminating unit 4 and themulti-direction illuminating unit 5 may be used selectively inaccordance with the kind of wafers 1. For example, the illuminating unit3 and the illuminating unit 4 are used to effectively utilize the effectof the later-appearing spatial filter for memory products. For logicproducts, on the other hand, the multi-direction illuminating unit 5 isemployed to effectively reduce the speckle noise. The illuminating unit3 and the illuminating unit 4 are used for the wafers in the depositionfilm process and the multi-direction illuminating unit 5 is used for thewafers in the etching process.

Next, the objective lens 6 has the function of condensing the scatteredrays of light from the region illuminated by the illuminating units 3and 4 or by the multi-direction illuminating unit 5. Incidentally, thisobjective lens 6 must be subjected to aberration correction in thewavelength band of illumination light. However, the construction of theobjective lens 6 may be of a refraction type lens or when anillumination light source of a wavelength not transmitting through thelens is used, a reflection type lens constituted by reflecting plateshaving a radius of curvature may be used, too.

FIG. 5 is a detailed explanatory view of the multi-region detecting unit7. FIG. 5A is a side view of the multi-region detecting unit 7 and FIG.5B shows its top. Referring to FIG. 5, the multi-region detecting unit 7includes a beam splitter 701, a detector 702, relay lens group 703, 704and 706, a spatial filter 705 and a polarization detecting element 707.The relay lens group 703 and 704 has the function of condensing the raysof light leaving the objective lens 6 and condensing also a Fouriertransform image of rays of light scattered by the wafer 1 to theposition of the spatial filter 705. The relay lens group 706 has thefunction of forming an image of the rays of light passing through thespatial filter 705 to the detector 702. Here, an optical path 2501represents the rays of light scattered by the illumination region 2204and an optical path 2502 represents the rays of light scattered by theillumination region 2205. In the case of illumination by themulti-direction illuminating unit 5, the rays of light are scatteredlight at the positions corresponding to the illumination region 2204 andthe illumination region 2205.

Here, the spatial filer 705 is used to optically remove information ofthe circuit pattern on the wafer 1. The Fourier transform image of thecircuit pattern on the wafer 1 is formed by condensation patterns at theposition corresponding to the wavelength of illumination light, theillumination angle and a repetition pitch of the circuit patterns. Thespatial filter 705 shades the rays of light of the condensation pattern.The rays of light of the circuit pattern of the portion corresponding tothis condensation pattern can be prevented from reaching the detector702. Because the condensation pattern of the Fourier transform imagechanges with the optical condition and with the kind of the circuitpattern, the spatial filter 705 must have the function of being able tochange the shading position.

Next, examples of the spatial filter 705 will be explained withreference to FIGS. 6A and 6B and FIGS. 7A and 7B. The example shown inFIGS. 6A and 6B is an example of the spatial filter on a plane (opticalaxis: Z direction) vertical to the optical axis. The example shown inFIGS. 6A and 6B includes a plurality of shading plates 2601, two springs2602 and two supporting rods 2603. The shading plate 2601 is formed of ametal sheet but the shading plate is not limited to the metal sheet andother materials can be used as long as they have the shading function.

Both ends of the shading plate 2601 are put on the spring 2602 and bothends of the spring 2602 are disposed on the supporting rods 2603. FIG.6A shows the condition where a mutual pitch of a plurality of shadingplates 2601 (distance between the shading plates) is set to p1. Incontrast, FIG. 6B shows the condition where the spring 2602 is stretchedas the supporting rod 2603 is moved in the Y direction and the pitch ofthe shading plate 2601 changes to p2. The optical axis exists in the Zdirection.

In the example shown in FIGS. 6A and 6B, therefore, the shading positioncan be changed in the Y direction by changing the mutual gap of the twosupporting rods 2603.

FIG. 7 shows another example of the spatial filter 705 that uses aliquid crystal device. FIG. 7A shows the side surface of the spatialfilter 705 and FIG. 7B shows the top. The polarization direction ofincident light of each cell is changed by an impressed voltage in theliquid crystal device and a specific polarization component can beremoved, that is, shaded, by a polarizing plate on the outgoing side.The advantage brought forth by using the liquid crystal device in theexample shown in FIG. 7 is that the shading position can be changedtwo-dimensionally by the impressing condition of the voltage.

The polarization detecting device shown in FIG. 5 is a polarizing plate.However, it is not always necessary and can be removed from the opticalpath. The detector 702 has the function of photo-electrically convertingincident light. An example of the detector 702 is an image sensor, whichmay be one-dimensional CCD sensor, a TDI (Time Delay Integration) imagesensor or a photo multiplier. Two-dimensional CCD sensors such as a TVcamera may be used and a high sensitivity camera such as EB-CCD cameramay be used, too. A sensor the speed of which is increased by dividing adetection pixel of the CCD into a plurality of TAP may be used, as well.Furthermore, a surface irradiation type sensor which conductsirradiation from the CCD surface may be used and a back surfaceirradiation type sensor on the opposite side to the CCD surface can beused. The back surface irradiation type is preferred for wavelengthsshorter than ultraviolet light.

As a selection method of the detector 702, a TV camera or a CCD linearsensor is preferably used to constitute an economical inspectionapparatus. When weak light is detected with high sensitivity, it isadvisable to use a TDI image sensor, a photo multiplier or an EB-CCDcamera. The advantage of the TDI image sensor is that the SNR of thedetection signal can be improved by adding a plurality of times thedetection signal.

Incidentally, when the TDI image sensor is used, the sensor ispreferably driven in synchronism with the operation of the conveyingsystem 2. When a high speed operation is necessary, a sensor having aTAP construction is preferably selected. When a dynamic range of therays of light received by the detector 702 is great, or in other words,when the rays of light inviting saturation of the sensor are incident, asensor having as an accessorial function the anti-blooming function ispreferably used.

Next, FIGS. 8 and 9 show the construction when a photo multiplier isused for the detector 702. FIG. 8A shows a side surface of the photomultiplier unit and FIG. 8B shows its lower surface. When the photomultiplier is used, it is advisable to use a sensor having a pluralityof photo multipliers aligned in a unidimensional direction as shown inFIG. 8. According to this construction, the photo multipliers can beused as the unidimensional sensor having high sensitivity and canconduct high sensitivity inspection. As the construction in this case, amicro-lens 2802 is fitted to the photo multiplier 2801 on the side ofincident light as shown in FIG. 8A to condense the rays of incidentlight to the photo multiplier 2801. The micro-lens 2802 has the functionof condensing the rays of light within a range equal to the photomultiplier surface to the photo multiplier. 2801.

It is also possible to employ the construction in which an optical fiber2902 is fitted through a holder 2901 disposed on the downstream side ofthe micro-lens 2802 and a photo multiplier 2801 is fitted to the outputend of the optical fiber 2902 as shown in FIG. 9. In this case, sincethe diameter of the optical fiber 2902 is smaller than the diameter ofthe photo multiplier 2801, the sensor pitch can be decreased incomparison with the example shown in FIG. 8 and a sensor having highresolution can be provided.

FIG. 10 shows an example of the arrangement of the detector 702. Thedrawing shows the state where the detector 702 is projected to thesurface of the wafer 1. In the projection images 3001 and 3002 of thedetector 702 that are shown in FIG. 10A, the detector 702 is arranged insuch a fashion as not to cause a deviation in the Y direction. In theexample shown in this drawing, the circuit pattern on the wafer 1 passesthrough the same pixel f two detectors 702.

On the other hand, FIG. 10B shows an example of the arrangement wherethe projection images 3001 and 3002 are deviated by dy. According to thearrangement shown in FIG. 10B, the circuit pattern on the wafer 1 passesthrough the position deviated by dy in the two detectors 702.

The effect brought forth by synthesizing the detection signals obtainedby the arrangement shown in FIG. 10A will be explained. FIG. 11 showssignals when the same foreign matter on the wafer 1 is detected by twodetectors A and B. In comparison with the SNR of the foreign matter bythe single detector, the SNR of the foreign matter can be improved byaveraging the two detection signals as shown in FIG. 11 for thefollowing reason. Because the optical noise of the background occurs atrandom timing, the optical noise can be reduced by averaging the twodetection signals. However, because the occurrence of the foreign mattersignal is not random, the signal drop of the foreign matter signal doesnot occur. This also holds true of the circuit pattern signal (signal ofthe pattern the signal reduction of which cannot be made by the spatialfilter). In consequence, the SNR of the circuit pattern signal can beimproved, the stable signals can be acquired and the defect can bedetected at high sensitivity by signal processing that will be laterdescribed.

According to the arrangement shown in FIG. 10B, on the other hand, asignal having higher resolution can be obtained than the detectionsignal acquired by the signal detector by synthesizing the detectionsignals at deviated positions. In other words, insensitive zones occuramong pixels in a detector having a plurality of pixels aligned such asa CCD sensor. When the two detectors are deviated from each other by ½pixel, the insensitive zone of one of the detectors can be detected bythe other detector and can be thus eliminated. Therefore, signals havingresolution that is about twice the resolution of the signal detector canbe obtained by synthesizing these detection signals.

The example given above represents the case where the detection signalsof the detectors A and B are averaged but processing other thanaveraging processing can be employed, too. For example, a signal havinga lower noise level can be employed by adopting the smaller one of theoutput signals of the detectors A and B.

When the signals of both detectors A and B are compared and their ratiois outside a predetermined range, there is the possibility that eitherone, or both, of the detectors A and B are in trouble. Therefore, alarmdisplay is made by using suitable alarm means or the result acquired isdiscarded and output is made with notice to the effect that reliabilityis low so that re-measurement can be made automatically.

Next, the detail of the signal processing circuit 8 will be explainedwith reference to FIG. 12. Referring to FIG. 12, the signal processingcircuit 8 includes a gradation converting unit 801, a filter 802, adelay memory 803, a signal synthesizing unit 804, a delay memory 805, apositioning unit 806, a comparison processing unit 807, a CPU 808 andstoring unit 809.

Subsequently, the operation of the signal processing circuit 8 will beexplained. First, the detection signals 3201 and 3202 obtained by thedetector 702 are subjected to gradation conversion by the gradationconverting unit 801 of the signal processing circuit 8. This gradationconversion is analogous to the one described in JP-A-8-320294, forexample. The gradation converting unit 801 corrects the signal by linearconversion, logarithmic conversion, exponential conversion, polynomialconversion, and so forth. At this time, the detection signals 3201 and3202 may be subjected to mutually different conversions. For example,different conversions are carried out to normalize the output signal ofthe gradation converting unit 801 when the photoelectric conversioncharacteristics of the two detectors 702 are mutually different.

Next, the filter 802 is the one that removes noise unique to the opticalsystem from the signal subjected to the gradation conversion by thegradation converting unit 801 and is an averaging filter, or the like.The delay memory 803 is a signal delaying unit for delaying the signalused for the signal synthesizing processing executed in a later stageand has the function of storing the signals outputted from the filter802 in a repetition unit constituting the wafer 1, that is, a unit ofone cell or a plurality of cells or one die or a plurality of dies.

Here, the cell is a repetition unit of the circuit pattern inside thedie. Incidentally, the filter 802 may be applied after passing throughthe delay memory 803.

Next, the signal synthesizing unit 804 has the function of synthesizingthe signal obtained by processing the detection signal 3201 and thesignal obtained by processing the detection signal 3202. For example, itis the processing for averaging the signals corresponding to the sameposition on the wafer 1. The random noise can be reduced and the stablesignal can be obtained by averaging the output signals of the twodetectors A and B. The delay memory 805 is a signal storing unit fordelaying the signal used for positioning processing that is executed ina later stage.

The positioning unit 806 has the function of detecting the positioningerror between the signal outputted from the signal synthesizing unit 804(detection signal obtained from the wafer 1) and the delay signalobtained from the delay memory 805 (reference signal as reference) andconducting positioning in a pixel unit or below the pixel unit. In otherwords, the positioning unit 806 conducts positioning of the signal toclarify from which position in the detected region the signal exists insubstantially the same region on the wafer 1 for the signals detected bythe two detectors with timing deviated from each other.

The comparison processing unit 807 is the unit for detecting the defecton the basis of the difference of the feature volumes by comparing thedetection signals outputted from the positioning unit 806. Layoutinformation of the device on the wafer 1 is inputted in advance from theinput/output unit 10 and the CPU 808 generates a defect position andfeature volume data in the layout on the wafer 1 and stores them in thestoring unit 809. The defect position and the feature volume data aresent to the ADC unit 9 and the input/output unit 10, whenever necessary.Incidentally, the detail of the comparison processing unit 807 may bethe same as the one disclosed in JP-A-61-212708 and includes, forexample, a difference signal detection circuit of a positioned signal, acircuit for detecting non-coincidence by binarizing the differencesignal and a feature volume extraction circuit for calculating an area,a length (projection length) and coordinates from the binarized output.

The ADC (Automatic Defect Classification) unit 9 has the function ofclassifying the kinds of detected matters from the signals detected bythe inspection apparatus according to the first embodiment of theinvention. Its operation is as follows.

First, the signal acquired by the detector 702 is transmitted to thesignal processing circuit 8 and the ADC unit 9. The signal processingcircuit 8 carries out the defect defection processing. When the defectis judged as existing, a defect detection flag and the feature volumeprocessed by the signal processing circuit 8 are transmitted to the ADCunit 9. When receiving the defect detection flag, the ADC unit 9classifies the kind of the defect from the feature volume of the defectportion on the basis of the signal obtained by the detector 702 and thedata transmitted from the signal processing circuit 8. Theclassification method maps various kinds of feature volumes onpoly-dimensional coordinate axes and divides the region by apredetermined threshold value. The defect kind of the data existing inthe divided region is set in advance and the kind of defect is decided.The defect kind so decided is transmitted as the classificationinformation to the input/output unit 10 and is displayed as the defectinformation.

The term “feature volume” described above means the sum of the signalvalues of the defect portion, the differentiation value of the signalvalue, the number of pixels, the projection length, the centroidposition, the signal values of normal portions compared, and so forth.The feature volumes associated with the position include the distancefrom the center of the wafer 1, the number of times of repetition of thewafer 1 per die, the position inside the die, and so forth.

Next, the input/output unit 10 will be explained. The input/output unit10 is an interface unit with users and is also an input/output unit ofdata and control signals. The input information from the users are thelayout information of the wafer 1, the names of processes, condition ofthe optical system mounted to the defect inspection apparatus accordingto the first embodiment of the invention, and so forth, for example. Theoutput information for the users includes the map of the defectdetection positions, the kind of the defects detected, the images, andso forth.

As explained above, the first embodiment of the invention employs theconstruction in which substantially the same region of the surface ofthe wafer 1 is detected at different timings by using two detectors andthe noise is eliminated by using the output signals from the twodetectors. According to this construction, a large number of rays ofillumination light are not irradiated simultaneously to the same regionon the wafer. Therefore, the invention can realize a pattern defectinspection apparatus, and a method for the apparatus, that can eliminatenoise resulting from other causes without inviting the occurrence of thenoise owing to interference of a large number of rays of illuminationlight and can detect minute defects on the sample with high sensitivitywithout generating the speckle noise in the signals.

Second Embodiment

Next, the second embodiment of the invention will be explained. In thissecond embodiment, the construction of the illuminating units 3 and 4 ofthe defect inspection apparatus is different from the construction inthe first embodiment. Since the rest of the constructions are the same,their detailed explanation will be omitted.

FIG. 13 shows the construction of the illumination of the secondembodiment for illuminating a plurality of regions on the wafer 1. Thedifference of the example shown in FIG. 13 from that of FIG. 2 residesin that whereas illumination is made from ±f directions with respect tothe X or Y direction of the conveying system 2 in the example shown inFIG. 2, it is made from the same direction, that is, from the directionof f=0 in the example shown in FIG. 13.

The advantage of the construction of the illuminating unit shown in FIG.13 is that the size of the construction of the apparatus can be reducedbecause the illumination direction and the longitudinal direction ofillumination are equal.

In other words, the second embodiment of the invention provides theeffect that the apparatus construction of the defect inspectionapparatus can be made small in addition to the similar effect of thefirst embodiment.

Third Embodiment

Next, the third embodiment of the invention will be explained. In thethird embodiment, the construction of the illuminating unit 3 of thedefect inspection apparatus is different from the construction in thefirst embodiment. Since the rest of the constructions are the same,their detailed explanation will be omitted.

FIG. 14 shows a schematic construction of the illuminating unit in thisthird embodiment. The third embodiment uses a plurality of light sourcesof the illuminating unit. In FIG. 14, an illumination light source 3401of a wavelength λ2 different from the wavelength λ1 of the illuminationlight source 301, a light power polarization adjusting unit 3402, acoherency reducing unit 3403, a condensation optical system 3405 and anoblique illumination mirror 3406 are arranged in place of theilluminating unit 4.

The functions of the light power polarization adjusting unit 3402, thecoherency reducing unit 3403, the condensation optical system 3405 andthe oblique illumination mirror 3406 are equivalent to those of thelight power polarization adjusting unit 302, the coherency reducing unit303, the condensation optical system 305 and the oblique illuminationmirror 306, respectively, and the difference resides only in thatwavelengths that are subjected to aberration correction are different inthe optical system.

The advantage brought forth by illumination with different wavelengthsis that influences of thin membrane interference in the transparent filmformed on the surface of the wafer 1 can be reduced. In other words,because the change quantity of light power due to the thin membraneinterference of the wavelength λ1 and the light power change due to thethin membrane interference of the wavelength λ2 with respect to the filmthickness are different, the power volume changes can be averaged andstable signals can be obtained when illumination is made with differentwavelengths.

This means that the third embodiment of the invention provides theeffect that the power volume changes can be averaged and stable signalscan be obtained in addition to the effect similar to that of the firstembodiment.

Fourth Embodiment

Next, the fourth embodiment of the invention will be explained withreference to FIGS. 15 to 17. In the fourth embodiment, the constructionof a multi-direction illuminating unit is different from themulti-direction illuminating unit 5 in the first embodiment. The rest ofthe constructions are equivalent to those of the first embodiment.

FIG. 15A shows the side of the multi-direction illuminating unit in thefourth embodiment and the illuminating unit includes total reflectingmirrors 3501, 3504, 3507, 3512 and 3514, partial mirrors 3502, 3503,3508, 3509, 3510, 3511 and 3513, a polarization controlling unit 3505and a relay lens 3506.

Next, the operation will be explained. The rays of light reflected bythe mirror 503 are branched into the rays traveling in the direction ofthe mirror 3509 and the rays traveling in the direction of the mirror3510. The rays of light incident into the mirror 3510 are branched intothe rays traveling in the direction of the mirror 3511 and the raystraveling in the direction of the polarization controlling unit (Zdirection shown in FIG. 15).

Similarly, the rays of light are branched by each partial mirror intotwo directions and are reflected by each total reflecting mirror intoone direction. The rays of light reflected by the mirrors 3402, 3503,3504, 3510, 3511, 3512, 3513 and 3514 in the Z-axis direction aresubjected to polarization adjustment by the polarization controllingunit 3505 and are then condensed by the total reflecting mirror 3507 tothe focal plane of the objective lens 6 through the relay lens 3506.

FIG. 16 shows the mode of condensation. In FIG. 16, the rays ofcondensed light conduct illumination from 8 directions to the visualfield of the objective lens 6 so that all illuminations overlap with oneanother in the illumination region 3601.

Here, the reflection factor of each partial mirror is changed so thatthe intensity of light incident to the total reflecting mirror 3507 issubstantially equal. The polarization controlling unit 3505 isconstituted by a ½ wavelength plate and a ¼ wavelength plate. Theadvantage of this fourth embodiment is that the polarization directionof each illumination irradiated to the wafer 1 can be controlled by thepolarization controlling unit 3505.

For example, illumination in total directions can be adjusted to Spolarized light, and S polarized and P polarized light can be mixed inaccordance with the illumination direction. The polarization directionof illumination light may be decided in accordance with the surfacecondition of the wafer 1.

FIG. 17 shows another example of the total reflecting mirror 3507.Whereas the example shown in FIG. 15 uses a sheet-like mirror for thetotal reflecting mirror 3507, the example shown in FIG. 17 uses aparabolic mirror 3701 for condensation. The advantage of the sheet-likemirror 3507 is that an economical optical component can be used and thecost of the apparatus can be reduced. On the hand, the advantage of theparabolic mirror 3701 is that it is effective when illumination of highluminance is necessary because the mirror can efficiently condense therays of illumination light.

The fourth embodiment of the invention provides the effect that thepolarization direction of each illumination irradiated to the wafer 1can be controlled in addition to the effect analogous to that of thefirst embodiment.

The embodiment given above explains the method for conductingmulti-direction illumination from eight directions to the visual fieldof the objective lens 6 but the illumination direction need not alwaysbe eight directions but may be a plurality of directions. Theillumination direction of the rays of illumination light from the eightdirections can be selected by shading them by a shutter, not shown inthe drawing.

Fifth Embodiment

The fifth embodiment of the invention will be explained with referenceto FIG. 18. In the fifth embodiment, the construction of a multi-regiondetecting unit is different from the multi-region detecting unit 7 inthe first embodiment. The rest of the constructions are equivalent tothose of the first embodiment.

FIG. 18A shows the side surface of the multi-region detecting unit 7 inthe fifth embodiment and FIG. 1B shows its upper surface. Themulti-region detecting unit shown in FIG. 5 executes detection bydividing a plurality of illumination regions of the wafer 1 by the beamsplitter 702 into transmission light and reflected light but theembodiment shown in FIG. 18 conducts detection by reflectingillumination light into two directions by a triangular prism 3801.

The fifth embodiment of the invention provides the effect thataberration due to detection of transmission light need not be madebecause reflected light of the triangular prism 3801 is detected, andthe construction of the apparatus can be made economical in addition tothe effect analogous to the first embodiment.

Sixth Embodiment

Next, the sixth embodiment of the invention will be explained withreference to FIG. 19. In this embodiment, a light power evaluating unit3901 is added to the first embodiment (ADC unit 9 is omitted) and therest of the constructions are analogous to those of the firstembodiment.

In FIG. 19, a detector 3902 and a detector 3903 are the same detector asthe detector 702 shown in the first embodiment. The sixth embodiment ofthe invention represents the example where one of the two detectors 3902and 3903 is used as a detector for measuring scattered light power fromthe wafer 1 while the other is used for detecting defects.

The operation of the sixth embodiment will be explained. In FIG. 19, theconstruction in which illumination light is irradiated to the wafer 1,the detector 3902 or 3903 detects the signal and the signal processingunit 8 detects the defect is the same as in the first construction. Inthe sixth embodiment of the invention, the construction in whichillumination light power of the illumination region corresponding to thedetector that makes detection in a later stage on the basis of detectionlight power of the detector making detection in an early stage when thewafer 1 is scanned by the conveying system 2 is added.

In FIG. 19, the detector 3902 makes detection of the same position ofthe wafer 1 during scanning in the scanning direction 3904 at an earliertiming than the detector 3903, and the detector 3903 conducts detectionat an earlier stage in the scanning direction 3905 than the detector3902. At this time, the region detected by the detector 3902 isilluminated by the illuminating unit 3 and the region detected by thedetector 3903 is illuminated by the illuminating unit 4.

First, in the scanning direction 3904, the signal detected by thedetector 3902 is sent to the light power evaluating unit 3901, whichmeasures scattered light power from the wafer 1. When the signal getsinto saturation in this instance, a signal representing that light poweris excessive is outputted from the controller 11 to the light powerpolarization adjusting unit 402 to lower light power of the light powerpolarization adjusting unit 402. When the signal detected by thedetector 3902 is small, a signal for increasing light power outputtedfrom the controller 11 to the light power polarization adjusting unit402. In consequence, illumination light power of the illuminating unitis adjusted to an optimal value and the signal quantity detected by thedetector 3903 is optimized.

In the case of the scanning direction 3905, on the other hand, the lightpower evaluating circuit 3901 measures scattered light power from thewafer 1 on the basis of the signals detected by the detector 3903 andthe light power polarization adjusting unit 302 adjusts light power andoptimizes irradiation light power of the illuminating unit 3.

Because illumination light power to the wafer 1 can be adjusted on thereal time basis by the operation described above, scattered light powerincident to the detector 3902 or 3903 can be adjusted on the real timebasis. Therefore, an optimal detection signal can be always detectedwithin the dynamic ranges of the detectors 3902 and 3903 and variouscircuit patterns of the wafer 1 can be inspected with high sensitivity.

The sixth embodiment of the invention provides the effect that thedynamic range of the fine defect detector can be enlarged and variouskinds of fine defects can be detected in addition to the effectsanalogous to those of the first embodiment.

The embodiment described above explains an example of adjustment ofillumination light power. However, detection light power may be adjustedby interposing ND filters between the beam splitter 701 and the detector3902 and between the beam splitter 701 and the detector 3903 or the gainof the analog signals of the detector 3902 or the detector 3903 may beadjusted. The method that adjusts the gain of the detector provides theadvantage that the operation speed can be increased.

Seventh Embodiment

Next, the seventh embodiment of the invention will be explained withreference to FIG. 20. The seventh embodiment is constituted by addingbeam splitters 4002 and 4003, Fourier transform image observing units4002 and 4005 and a Fourier transform image analyzing unit 4005 to thefirst embodiment of the invention (ADC unit 9 is omitted). In theseventh embodiment, one of the optical paths branched by the beamsplitter 701 images the Fourier transform image and decides a spatialfilter and the other optical path conducts defect detection. Thedetectors 3902 and 3903 are of the same type as the detector 702 in thesame way as the second embodiment. The rest of the constructions are thesame as those of the first embodiment.

The operation of the seventh embodiment will be explained. In FIG. 20,illumination light is irradiated onto the wafer 1, the detector 3902 or3903 detects the signal and the signal processing unit 8 detects thedefect in the same way as in the first embodiment. The relation of thescanning direction, the timing of the signals detected by the detectors3902 and 3903 and the illuminating units 3 and 4 is the same as that ofthe second embodiment.

Scattered light from the circuit pattern on the wafer 1 illuminated bythe illuminating unit 3 or 4 passes through the objective lens 6 and isbranched by the beam splitter 701 into the optical paths explained withreference to FIG. 5. The rays of illumination light branched by the beamsplitter 701 towards the detector 3902 is branched by a beam splitter4001. Reflected rays of light pass through the Fourier transform imageobserving unit 4002 and a Fourier transform image is imaged.

On the other hand, transmitted light of the beam splitter 4001 isdetected as the image of the wafer 1 by the detector 3902. Here, theFourier transform image observing unit 4002 is constituted by relaylenses and a TV camera that are not shown in the drawing. The rays oflight branched by the beam splitter 701 towards the detector 3903 aresubjected to the image formation by the Fourier transform imageobserving unit 4003 and the detector 3903 in the same way as the rays oflight branched towards the detector 3902.

Next, the signals acquired from the Fourier transform image observingunits 4002 and 4004 are sent to the Fourier transform image analyzingunit 4005. Here, the Fourier transform image analyzing unit 4005 has thefunctions of analyzing the Fourier transform image taken, recognizingthe Fourier transform pattern and calculating data having a suitablespatial filter form. The data calculated by the Fourier transform imageanalyzing unit 4005 are position information to be shaded by the spatialfilter.

The data calculated by the Fourier transform image analyzing unit 4005are sent to the controller 11, can control the spatial filter 705 (notshown in FIG. 20) and can also change the shape of the spatial filter705 on the real time basis.

The spatial filter 705 must be removed from optical paths that are notused for the defect detection.

Owing to the operations described above, scattered light from the wafer1 can be optically erased on the real time basis and various kinds ofcircuit patterns of the wafer 1 can be inspected with high sensitivity.

In other words, the seventh embodiment of the invention provides theeffects that scattered light from the wafer 1 can be optically erased onthe real time basis and various kinds of circuit patterns of the wafer 1can be inspected with high sensitivity in addition to the effectsanalogous to those of the first embodiment.

Eighth Embodiment

Next, the eighth embodiment of the invention will be explained withreference to FIGS. 21 to 25. The eighth embodiment relates to a defectinspection apparatus formed by adding a construction for inspecting abevel portion of the wafer 1 to the defect inspection apparatus of eachof the first to seventh embodiments. Here, the term “bevel portion”represents an end face portion of the wafer 1 shown in the sectionalview of FIG. 22 and falls within the range of about 3 mm from the edgeof the wafer 1.

As shown in FIG. 21, the eighth embodiment includes a bevel inspectingunit 12 in addition to the embodiment shown in FIG. 1 and the rest ofthe constructions are the same as those of FIG. 1.

FIG. 23 shows the detail of the bevel inspecting unit 12. In the eighthembodiment, the case where the bevel portion is inspected by using amechanism accessorial to the apparatus, for detecting a referenceposition in the rotating direction of the wafer 1, will be explained.

FIG. 23A shows the side surface of the bevel inspecting unit 12 and FIG.23B shows its top surface. The bevel inspecting unit 12 includes a waferchuck 1201, a rotary motor 1202, a sheet-like beam emitting unit 1203, asheet-like beam receiving unit 1204, illumination light sources 1205, aTV camera 1206 and 1207, a data storing unit 1208 and relay lenses andmirrors both of which are not shown in the drawing.

The operation of the eighth embodiment will be explained. In FIGS. 21 to23, the wafer 1 is taken out from a wafer cassette by a robot arm, notshown, and is fixed by vacuum adsorption on the wafer chuck 1201. Next,the sheet-like beam emitting unit 1203 emits a sheet-like beam.

Here, the sheet-like beam is a beam that is elongated in a directionparallel to the radial direction of the wafer 1 and the size of the beamand its position are set in such a fashion that the edge of the wafer 1transversely crosses the sheet-like beam. The sheet-like beam emittedfrom the emitting unit 1203 is received by the sheet-like receiving unit1204. The wafer 1 is rotated round the Z axis as its center by therotary motor 1202 disposed on the wafer chuck 1201.

A hollow cut called “notch” is formed in the wafer 1 as the reference ofthe rotating direction. Therefore, the shading ratio of the sheet-likebeam decreases at the notch portion when the wafer 1 is rotated whereasthe beam reception quantity by the sheet-like beam receiving unit 1204increases at the notch portion.

FIG. 24 shows an example of the change of the beam reception quantity atthis time. In FIG. 24, the abscissa represents the rotating angle movedby the rotary motor 1202 and the ordinate represents the beam receptionquantity of the sheet-like beam receiving unit 1204. As described above,the transmission factor increases at the notch portion when the wafer 1is rotated and the beam reception quantity increases. The waveform ofthe increase of the beam reception quantity changes depending on theshape of the notch but is generally trapezoidal or triangular. Afterthis waveform data is acquired, the portion at which the beam receptionquantity increases is recognized as the region of the notch and thecenter of this notch region is recognized as the center of the notch. Inthis way, the position of the notch as the reference of the rotatingdirection of the wafer 1 can be detected.

The eighth embodiment of the invention conducts detection of the bevelportion simultaneously with the detecting operation of the rotationreference position described above. After the wafer 1 is fixed asdescribed above, the beam is emitted from the illumination light source1205 and the bevel portion of the wafer 1 is illuminated from thedirection P with respect to the center axis of the imaging region of theTV camera 1206. At this time, illumination light may be either whitelight or a laser beam. When any defect exists, strong scattered lightoccurs in the bevel portion illuminated by the illumination light source1205 and is detected by the TV camera 1206.

On the other hand, scattered light is weak in the normal portion atwhich no defect exists and the TV camera 1206 detects nothing. The raysof light detected by the TV camera 1206 are sent to the data storingunit 1208 and scattered light power from the bevel portion iscalculated.

FIG. 25 shows an example of the signal change of the bevel portion. InFIG. 25, the abscissa represents the rotating angle moved by the rotarymotor 1202 and the ordinate represents the signal value of the TV camera1206. As shown in FIG. 25, the signal value becomes small at the normalportion and large at the defect portion. A pre-determined thresholdvalue is set to this waveform and signals exceeding the threshold valueare judged as being defect portions. The inspection of the bevel portionbecomes thus possible.

Information of the defect detected is transmitted to the input/outputunit 10 and is displayed on the display. The defect information is thedefect position and the image of the TV camera 1206, for example. Theadvantage brought forth by outputting the image of the defect portion isthat the defect portion becomes recognizable more easily.

As for the regions that cannot be imaged by the TV camera 1206, on theother hand, a TV camera 1207 may be added for imaging so as to detectthe defect. The operation of the TV camera 1207 is the same as that ofthe TV camera 1206.

After sensing of the rotation reference position and the inspection ofthe bevel are completed, the wafer 1 is transferred to the conveyingsystem 2 by the robot arm, not shown, and the wafer surface is inspectedby any of the inspection apparatuses of the first to seventhembodiments.

Having the construction described above, the eighth embodiment of theinvention can inspect highly precisely the surface of the wafer 1 in thesame way as in the first to seventh embodiments and can also evaluatewith high sensitivity the bevel portion of the wafer 1.

Incidentally, it would be obvious to those skilled in the art that theembodiments described above are mutually applicable.

The invention can be applied not only to the inspection of semiconductorwafers but also to the inspection of thin film substrates, photo masks,PDP, and so forth.

It should be further understood by those skilled in the art thatalthough the foregoing description has been made on embodiments of theinvention, the invention is not limited thereto and various changes andmodifications may be made without departing from the spirit of theinvention and the scope of the appended claims.

The invention claimed is:
 1. An inspection apparatus which inspects adefect of a sample, comprising: an illumination system which forms afirst illumination area on a surface of said sample and a secondillumination area of said surface; a detection system which has a firstfield of view for said first illumination area and a second field ofview for said second illumination area though an objective lens, andwhich includes a first detector corresponding to said first field ofview and a second detector corresponding to said second field of view,said first detector being configured to output a first scattered signaland said second detector being configured to output a second scatteredsignal; and a processing system which processes at least one of saidfirst scattered signal and said second signal, wherein said processingsystem includes a first gray level changing unit which changes a firstgray level of said first scattered signal, and a second gray levelchanging unit which changes a second gray level of said second scatteredsignal; and a first normalizing filter for said first scattered signal,and a second normalizing filter for said second scattered signal.
 2. Theinspection apparatus according to claim 1, wherein said processingsystem integrates said first scattered signal with said second scatteredsignal.
 3. The inspection apparatus according to claim 2, wherein saidprocessing system acquires a normalized signal using said firstscattered signal and said second signal.
 4. The inspection apparatusaccording to claim 3, wherein said processing system includes a delaymemory, and is configured to adjust a position associated with saidnormalized signal using a delayed signal from said delay memory.
 5. Theinspection apparatus according to claim 4, wherein said processingsystem detects a defect using a position adjusted signal determined bysaid processing system.
 6. The inspection apparatus according to claim1, wherein said processing system processes said first scattered signaland said second scattered signal individually.
 7. The inspectionapparatus according to claim 6, wherein said processing system includesa first delay memory for said first scattered signal, and a second delaymemory for said second scattered signal.
 8. The inspection apparatusaccording to claim 1, wherein said illumination system illuminates saidsample with light from a plurality of directions.
 9. The inspectionapparatus according to claim 8, wherein said illumination system changespolarization directions of said light from a plurality of directions.10. The inspection apparatus according to claim 9, wherein saidpolarization directions are S polarization and P polarization.
 11. Theinspection apparatus according to claim 9, wherein said illuminationsystem includes a parabolic mirror.
 12. The inspection apparatusaccording to claim 9, wherein said detection system includes apolarization detecting element.
 13. The inspection apparatus accordingto claim 8, wherein said illumination system changes wavelengths of saidlight from among the plurality of directions.
 14. The inspectionapparatus according to claim 8, wherein said illumination systemilluminates said sample using a fiber system.
 15. The inspectionapparatus according to claim 14, wherein said fiber system changeslengths of optical paths through which said light from the plurality ofdirections pass.